Seasonal gift of great geese almost cooked (6,3)
I believe the answer is:
easter egg
'seasonal gift' is the definition.
(I've seen this before)
'great geese almost cooked' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'cooked' is an anagram indicator.
'great'+'geese'='greatgeese'
'greatgeese' with its last letter taken off is 'greatgees'.
'greatgees' anagrammed gives 'EASTER EGG'.
'of' is the link.
(Other definitions for easter egg that I've seen before include "festive gift" , "Programmer's surprise" , "Seasonal fare" , "Seasonal present" , "Seasonal gift" .)